Process for coating sheet materials



Patented June 25, 1946 PROCESS FOR COATING SHEET MATERIALS Peter J. Massey and Lothian M. Burgess, Chicago, Ill., assignors to H. P. Smith Paper Company, Chicago, Ill., a corporation of Illinois N Drawing.

Application September 27, 1944,

Serial N0. 556,094

Claims. (Cl. 117168) This invention relates to the laminating of sheet materials such as paper, regenerated cellulose films, cellulose ether or ester films, vinyl polymer films, foil, rubber and rubber derivatives, webs and the like or similar sheets or films to each other and/or to themselves in two or more plies.

This invention is particularly directed to a process for laminating such sheet materials with heat liqueiiable, thermoplastic materials having the properties of rendering such laminated sheets moisture vaporproot and/or waterproof.

It is generally known that waxy or waxlike materials, particularly the petroleum or mineral oil derived waxes, are among the best known moisture proofing materials available, These include the parafiin waxes, the petroleum fjellies and waxes, all hereinafter referred to as waxes, with or without modifying agents or any of the compatible resins, rosins, gums, film formers, elastomers, etc., natural, factitious or wholly synthetic.

The use or application of these waxes alone for laminating, for example, paper which is pervious, is practically impossible without the addition of a material which increases the viscosity of the wax at and above its melting point so that it may be applied as a continuous film over one of the sheets without undue penetration or absorption. When applied alone, these waxes would permeate into the fibres and would not act either as an adhesive laminant or as a barrier to the passage of moisture. Additionally very important is necessity to minimize bleeding or strikethrough at higher temperatures, e. g., 140 F. in the finished product. I

Among the common materials for increasing viscosity of these waxes are the higher fatty acid soaps of metals such as aluminum oleate, palmitate or stearate and mixtures of these with varying ratios of aluminum to fatty acid. These metallic soaps are soluble in the petroleum waxes, or at least are dispersible therein, with the formation of jells with greatly increased viscosity at concentrations of about three percent (3%) by weight and upwards; increasing amounts of these metallic soaps greatly increase this viscosity in ratios exceeding a, straight line function. For

the a.

2 example, the following table is shown as illustrative:

TABLE I Viscosity at 280 F. with varying percentages of aluminum stearate in microwaa:

. [41 penetration and 146 F. melting point] Viscosity in However,. the viscosity increase is not permanent and great difiiculties have been encountered in the past when the compound is maintained at the elevated'temperatures necessary for application to the sheets or webs. Under such conditions there occurs a rapid degradation in viscosity.

Heretofore, in the preparation of aluminumstearate wax jells it has been the universal practice to prepare the compound in batch type operations in substantially the following manner: The wax is melted and the temperature raised to not over 180 F.; then the finely divided aluminum stearate powder is added and mechanically agitated until thoroughly dispersed. The temperature of the batch is then slowly raised and at 220F. or thereabouts the aluminum stearate begins to dissolve or disperse with the gradual formation of a jell of greatly increased viscosity reaching its maximum at about 275 F. or over. This compound is then ready for use, the batch being maintained at a temperature to give the proper viscosity, this temperature being dependent upon the amount of aluminum stearate and for greater amounts, must be higher.

A typical example of such prior practice is one in which four percent (4%) of aluminum stearate is dispersed in micro crystalline wax of 35 penetration at 77 F. (A. S. T. M. D-5-25) and F. melting'point (A. S. T. M. D-l27-30). This compound can be applied at a temperature of about 280 F. on a coating machine. At this temperature the laminating compound has a viscosity of 580 centipoises and spreads readily. A finished ing, this condition becomes aggravated and the l discovered that u a concentrated storage stable sheet made with this compound as initially preparedis highly resistant to the passage moisture vapor and when tested in an oven at 140! for four hours, showed no stain or bleedins through oi the compound. However, after a few ient proportion such as from about 40 to about 60% 01' the soap and from about 60 to about 40% hours the remainder oi the batch has lost 'suillcient viscosity to-cause it to strike-through the 7 sheet and, iurthermore, the finished sheet begins to show bleedihg at 140' 1". With continued heat-.

laminated sheets are Q int! In this iormer batch type of oper'atiomin which. large quantities oi compound must be made at one time, it is necessary to maintain the compound at the elevated temperature for ions periods oi time with recirculation and mechanical agitation. This period may be twenty-four hours or longer. The following table illustrates examples of this progressively ini'erior in by weight of the wax). It may be prepared y compmmding in a heated state in any type ofheavy duty mastic or dough mixer, rubber mixing rolls, a Banbury type mixer, or the like. and immediately cooled in any convenient size slab or formation. In this condition the concentrate is storage stable and not subjected to any condi-- tions which alter its subsequent Joli-forming characteristics. u t

i In one specific example for the purpose of illustration. and not limitation, of our process for continuously preparing a laminating compound using the concentrated jell, we may pump liquefied microcrystalline wax preheated at a temllit'rature of about 300 F. to a small mixer into which a /50 compound iell oi the same microwax and aluminum stearate, prepared as proviously described, is extruded through an ori- .iice,oraseriesoi'flneoriilcesorthelike,intoa mixer where it is immediately dispersed into the wax. .The aluminum stearate may be at room temperature or preferably somewhat heated to facilitate its-extrusion into filaments. The laminating compound containing the desired proportions of aluminum stearate is prepared by condegradation in viscosity:

Taste 1! Loss in viscosity after heating at 280' r. for ooryma time periods v I l vi Home heated or at no r.

iell because at the higher temperature the metalllc soapm'erely times or melts into hard, relatively insoluble lumps or pellets unless the temp rature is over 400 F. and this becomes practically impossible.

eessseseetesse centration of about 6% by weight, and the resultant dispersion is continuously withdrawn and de- It is not mis toiled P wdered aluminum stearatetoincre asetheviscosityoithe degraded As maximums from the iorescinsuand in accordance with our present invention, we have aluminum soap-wax .iell is first made. it may be dispersed or dissolved in proportioned amount direetly into am of wax preheated to the elevated temperature at which it is subsequently used, and continuously withdrawn and applied to for a non-penetrating lami'nant at a substan- As contrasted with the prior batch operation in which the entire bulk supply of compound is of necessity maintained for hours at elevated temeratures, in this new operation the finished com-- pound is maintained at the working. temperature only a matter or minutes. The drop in viscosity becomes-negligible, and even 11' degradation does occur, due to extraneous causes such as mechanical machine troubles or the like, causing temporary shut down, it could be immediately corrected by the addition of small quantities of the concentrated lell.

In the preparation of this Jell concentrate we may use, say, approximately 50% by weight of an aluminum soap of a higher fatty acid and the sur'iace oi't he'aheet material to provide there-- i tially constant viscosity, and that this operation may becarried out continuously.

trolling the rate .of pumping the wax and the rate of extrusion oi the aluminum stearate-wax concentrate to provide an aluminum stearate conlivered to the laminating machine at approximately the same rate that it is used on the paper.

It will be understood that although the final jell comprises a major proportion by weight of the wax component, that the'described metallic soap 'may be in the proportion of from about 3% to about 10% by weight, and that as previously indicated other modifying or plasticlzlng agents may also be included in like minor proportions. Also,

although thewithln jells and our method oi preparation and application have been particularly described for use as lamlnants, it will ,be understood by those skilled in the art that they may also be employed to good advantage in formation' and preparation of certain coated sheet materials.

We claim as our invention: 1. The method of applying an aluminum higher fatty acid soap-wax jell' to sheet material at a substantially constant-viscosity to provide a nonpenetrating laminant which comprises preparing a concentrated Jell of said components by heating and mixing said components together, cooling the concentrate immediately after its preparation to render it storage stable. and then continuously dispersing the concentrated jell in regulated proportions into preheated'wax and continuously withdrawing and applying the resultant dispert0 sion to a surface of the sheet material.

2. The method of applying a ieil comprising a major proportion by weight of a wax and a relatively small proportion by weight oi an aluminum stearate in heat liquefied condition to sheet mateto rial at a substantially constant viscosity to provide a non-penetrating laminant which comprises preparing a concentrated lell of said components containing a relatively large proportion of said aluminum stearate by heating and mixing said components together, cooling the concentrateimmediately after preparation to render it stor- 50% wax (or a composition of any other conveq- N relatively small proportion of the aluminum stearaeoaoos 5 ate and continuously withdrawing and applying the resultant dispersion to a surface of a sheet of the material to be laminated.

3. The method of applying a jail comprising a major proportion by weight of a wax and including from about 3%. to 10% b weight of an aluminum soap of ahigher fatty acid to sheet material at a substantially constant viscosity to provide anon-penetrating laminant andamoisture and moisture vapor-proof barrier which comprises initially preparing a concentrated Jell containing from about 40 to about 80% by weight of said aluminum soap from about 80 to about 40% by weight'of said wax by heating and mixing said components together, promptly cooling the conoentrate after preparation, and subsequently continuously dispersing the concentrate into a body 4 of wax preheated to application temperature in' proportioned amount to provide said-relatively smaller proportion of aluminum soap therein.

and continuously withdrawing and applying the .resultant dispersion to a surface of the sheet. material to be laminated.

I I 6 I centrate immediately after formation to render it storage stable, continuously a proportioned amount of said concentrate into a body of said wax preheated to a temperature of approximately 300 F. to form a Jell having an aluminum stearate content of from about 3% to about 10% by weight, and continuously withdrawing and applying the resultant dispersion,

at a substantially constant viscosity. to asurface of the sheet material to be laminated.

5. In the process of applying a wax aluminum soap or a higher fatty acid iell containing a major proportion by weight of said wax and from about 3% to about 10% of saidsoap whil'eheated to .a

viscosityregulated to-provide anon-penetrating v laminantfor sheet material and to form a substantially water and moisture vapor-proof barrier therefor, the steps which comprise heating and masticating said wax with a relatively high per 'centage of said soap to disperse and dissolve the 4 ,soap in the wax and to form a concentrated lell,

cooling said jeli to form a storage stable product.

. and thereaftercontinuously dispersing propor- 4. The method of forming a water and moisture vapor resistant sheet material laminate which comprises heating and intimately admixing a composition comprising from about 40 to about 1 60% by weight of aluminum stearate and from about 60% to about 40% by weightof a wax to form a concentrated iell and cooling the contioned amounts of said concentrated jell toa body of said wax preheated substantially to said application temperature to provide a Jell of'said lower soap content therein and'continuously withdrawing and mplying the resultant dispersion.

PETER-I. MASSEY. 'LOTHIAN M. BURGESS. 

